Test Methodology and Conditions:-
1. K-x on Tripod, Single AF mode, Central Single AF point selected, 2 second Timer with MLU;
2. Focal Lengths were tested as marked on the lenses, Av Exposure mode (and of course), Matrix Metering, No Exposure Compensation;
3. Portrait Custom Image -1, 0, 0, 0, Sharpness 0, AWB;
4. All images are resized to 3,999 pixels in width and no other re-touching is made to the images, All EXIF data preserved. Click Any of the Thumbnails will download the Large Size Image in a New Tab/Window. (Note: All Large Files!)
How to Measurbate, then? Download the Large Files and inspect the image centre and borders, note about contrast and sharpness, colour differences, distortion of the images and so on. Compare against one and each other(s) for the same/near focal length and see the effect of different apertures on the output Image Quality.
I do not test f/11 for all lenses as it is almost for sure that f/11 will not be as sharp as the diffraction limit is usually reached for APS-C DSLRs. My advice is that if you want to stop down, usually don't go beyond f/9.5 for optimal image quality! And, dust specks, if any, are more visible from f/11 and onwards, too.
Well, which lens(es) do I like more or most? Umm.., I think putting aside the different range and the physical characteristics of them (e.g., size and weight, design and operation, etc.), I would rate: FA 24-90 > DA 16-45 > FAJ 18-35 > SA 18-55 ~ DAL 18-55, as long as IQ is concerned, overall speaking.
Interestingly, according to Bojidar Dimitrov's K-mount Page, the optical formulae of the DAL 18-55 is the same as that of the DA 18-55II, whilst my "Samsung" Blue Ring SA 18-55 is the same as the original Pentax DA 18-55. So, my this comparison should show what are the actual difference(s) between the two optical formulae on the Image Quality, if any. But do bear in mind about sample variation as well for those cheapo kit lenses (of which the QC is not really good from my experiences).
What do you think, on the other hand? :-)
Lens Matching with My Navy K-x